Determination of non-volatile components in a liquid

ABSTRACT

The non-volatile matter content of a point is determined by passing a sample at a predetermined rate through a passage way containing inlet and outlet resistors, adding a predetermined amount of heat and measuring the resultant change in the resistors.

Bite Sttes atent 1 De Vittorio 1 Apr. 10, 1973 1 DETEe' ATHON OF NON VOLATHE COONENTS IN A LIQ 2 i a [75] Inventor: Joseph M. De Vittorio, Homewood,

Ill.

[73] Assignee: The Sherwin-Williams Company,

Cleveland, Ohio [22] Filed: Jan. 11, 1971 [21] Appl. No.: 105,680

Related U.S. Application Data [63] Continuation of Ser. No. 663,771, Aug. 28, 1967,

1,254,374 1/1918 Thomas ..73/204 946,886 1/1910 Thomas ..73/204 1,691,600 11/1920 Brush, Jr. et a1. ..73/204 FOREIGN PATENTS OR APPLICATIONS 858,024 12/1952 Germany ..73/190 OTHER PUBLICATIONS Weissberger Physical Methods Part I QD251W44, Interscience Publishers pg. 563

Primary Examiner.lames J. Gill Assistant Examiner-Herbert Goldstein Attorney.lohnston, Root, OKeeffe, Keil, Thompson and Shurtleff [57] ABSTRACT The non-volatile matter content of a point is determined by passing a sample at a predetermined rate through a passage way containing inlet and outlet resistors, adding a predetermined amount of heat and measuring the resultant change in the resistors.

13 Claims, 5 Drawing Figures A recent development in the art of applying or coat- 0 ing pigmentatious and other material upon objects to be coated, including, more particularly, the bodies of automotive vehicles, has been the provision of means for applying the coating material by electrodeposition from a bath comprising the solid pigmentatious material and a resinous binder to be deposited and a liquid carrier in which the material forms a suspension or solution and from which the material to be coated is deposited by electrolytic action. In such an arrangement, it will be obvious, that the bath in which elec trodeposition takes place will progressively lose its nonvolatile constituents as the same are deposited upon the object being coated, unless means are provided for replenishing the bath with material to replace that withdrawn from the bath and applied upon the objects being coated. It is especially true, in the interests of uniformity of application of material coated electrolytically from baths of the character mentioned, that the bath should at all times be maintained as precisely as possible with a constant concentration therein of material to be coated; and that means should desirably be provided for constantly measuring the concentrationof coating materials in the bath and to supply additional coating material in the bath to maintain the same at a desired concentration.

An important object of the present invention is to provide a new and improved method for measuring the concentration of NVM in a liquid.

A further object is to provide for continuously monitoring a suspension or solution, including baths for the electrolytic deposition therefrom, of coating material, so as to permit coating material to be added to the bath in order to maintain at a constant level the concentration of solid material in the bath.

Another important object is to provide a new and improved relatively simple type of apparatus for detecting changes in concentration of non-volatile materials in a liquid carrier therefor.

An additional object is to provide a new and improved apparatus for determining NVM in a liquid vehicle by measuring the difference in electrical resistance of thermally responsive electrical resistance elements in a sample of said vehicle containing NVM at different temperatures.

' Other objects and advantages of the invention will appear from the following description in conjunction with the accompanying drawings in which:

FIG. 1 is a diagrammatic showing of a system for monitoring the non-volatile constituents in a liquid carrier of the same in accordance with the teachings of the present invention;

FIG. 2 is a wiring diagram of a signal conditioner used in FIG. 1;

FIG. 3 is a partial sectional view of one form of apparatus adapted to be used in the system illustrated in FIG. 1;

FIG. 4 is a partial sectional view of another form of apparatus adapted to be used in the system illustrated in FIG. 1; and

FIG. 5 is a graph in which millivolts (mv) are plotted against percent NVM in order to illustrate one specific embodiment of the invention, as hereinafter more fully described.

In accordance with the invention it has been found that the non-volatile matter content of a mixture containing non-volatile matter in a liquid carrier can be determined by measuring the difference in electrical resistance of thermally responsive electrical resistance elements in a sample of said mixture at different temperatures. In carrying out the process, said sample is heated while flowing it through a tubular passageway and the electrical resistance of thermally responsive resistance elements before and after heating is measured, preferably by a pair of matched thermistors. The resistance elements, for example, the matched thermistors, can be connected to a signal conditioner which in turn can be connected to a suitable indicating device having an indicating scale calibrated to read percent by weight non-volatile matter. The process can be operated continuously or intermittently by flowing the mixture from a main body through a monitoring apparatus and thereafter returning it to the main body. By recycling the mixture continuously through the monitoring apparatus, the NVM concentration can be determined continuously and the concentration of the components of the main body of the mixture can be adjusted to compensate for removal of non-volatile matter. This is particularly important in an electrodeposition process such as in the electrodeposition of paints or other coating compositions becuase the non-volatile matter is being removed continuously from the electrodeposition bath.

In practicing the invention it is preferable to subject the mixture being tested to agitation just prior to bringing it into contact with the thermistors or other electrical element responsive to a change in electrical resistance. It is also desirable to provide an elongated heating zone of sufficient length to minimize the effect of rate of flow on temperature. In addition, it is desirable to provide a heating zone of such magnitude that the differential temperature before and after heating is sufficient to permit proper determination of the nonvolatile matter. For most practical purposes this temperature differential should be at least 10F. It can be much larger, for example, 20F., 30F., 40F, and on up to F., or higher. Normally, a differential of 10F. to 30F. is sufficient.

The monitoring apparatus comprises means forming a tubular passageway having an inlet and an outlet for a flowing mixture containing non-volatile matter in a liquid carrier, heating means for heating said mixture in said passageway, first thermally responsive electrical resistance measuring means in said passageway adapted to contact said flowing mixture before said mixture has been heated by said heating means, and second thermally responsive electrical resistance measuring means in said passageway adapted to contact said flowing mixture after said mixture has been heated by said heating means. The thermally responsive electrical resistance measuring means preferably comprises a pair of matched thermistors but other types of resistance elements can beemployed. The apparatus preferably comprises a pump for pumping the mixture through the tubular passageway. The apparatus also preferably comprises agitating means or a mixing chamber ahead of one or both of the thermally responsive electrical resistance measuring means.

In the foregoing description, the thermistors, or other types of resistance responsive elements, can also be called transducers. Generally speaking, therfore, the invention provides an apparatus and a method for determing the non-volatile matter content of a mixture containing non-volatile matter in a liquid carrier comprising container means for said mixture, heating means for heating said mixture in said container means, and electrical transducer means associated with said container means and responsive to changes in electrical resistance of transducers exposed to said mixture when said mixture is heated. In addition, it is desirable in the practical application of the invention to provide electrical signal means connected to said transducer means to translate said changes in electrical resistance into a measurement of change in concentration of nonvolatile matter in said mixture. This signal means may comprise a signal conditioning electrical circuit and an indicating device electrically connected to said circuit as hereinafter more fully described. The indicating means can be a millivolt meter calibrated to read directly, in terms of concentration of non-volatile matter in said mixture.

It will be recognized that resistance can be translated into voltage in accordance with the well known equation:

E=IR (I) wherein E is voltage or electromotive force, I is amperage or current, and R is resistance.

Thus, it will be seen that voltage change is proportional to resistance change.

The following equation can also be written:

AT=H/M( 2) wherein AT is the temperature differential, H is the heat input in calories, M is the mass in grams, and C,. is the specific heat of the mixture being evaluated.

Thus, in a paint system for electrodeposition where the mixture or coating composition consists of water and a cosolvent, together with resins, pigments and other non-volatile matter, the following equation can be written for the value of C where C is the specific heat of water which is l, and C, equals the specific heat of the non-volatile matter. If the mixture contains 10 percent non-volatile matter, i.e., resin plus pigment, and 90 percent water and the specific heat of the non-volatile matter is 0.6, C would then equal 0.96.

By keeping a constant mass and measuring the different differential in temperature to which a fixed mass of material is raised under conditions of fixed heat input to the mass, a given temperature rise will correspond to a given percentage of NVM.

In a paint system of the type described in which C equals 0.96 and AT equals 20F, each 0.08F. corresponds to 1 percent NVM. Where AT is 40F, each O.I6F. corresponds to 1 percent NVM.

Summarizing: (assuming T remains relatively constant) l. T =f(flow rate) =f (mass) =f(volume) (densi- 2. At constant BTU from heater AT (T T f(F where (F =flow rate 3. As F, increases the mass of paint exposed to the heater increases, therefore T would tend toward T as a limit. Conversely, as F, decreases, T would tend toward the heater temperature, T,,.

4. As the length, L, of the heater increases at a fixed cross sectional area and F,, the temperature T would tend toward T,, as a limit and AT would tend toward a maximum value.

5. If T,, and T are equal, then changes in F, will not affect T of AT.

While the length of the heater is subject to variation, it is preferable to use a heater which is at least eight inches long.

In the drawings, the invention is illustrated diagrammatically in FIG. 1 by a system for monitoring an electrodeposition paint wherein the paint supply 1 is connected by a conduit or pipe 2 to a mixing chamber 3 where the mixture is agitated in order to maintain uniform dispersion. The mixture then passes through a pipe or conduit 4 into an apparatus of the type illustrated in FIGS. 3 or 4 consisting of a thermistor 5 (T a tubular inlet passageway 6, a heater 7, and a tubular outlet passageway 8. In FIG. 1 the mixture is passed through a second mixing chamber 9, then through a tubular passageway into contact with a second termistor 11 (T After contacting the thermistor 11, the mixture passes through a pipe or conduit 12 to pump 13 which pumps it back into the paint electrodeposition bath through conduit or pipe 14.

The use of the mixing chambers 3 and 9 is optional and these are omitted in the specific types of apparatus illustrated in FIGS. 3 and 4.

The thermistors 5 and 11 are electrically connected to a signal conditioning device 15 which in turn is electrically connected to an indicating device 16 calibrated to read percentage by weight non-volatile matter.

In the form of the apparatus shown in FIG. 3, the mixture passes into contact with thermistor T in inlet passageway 17, then into contact with the heater 18 which has a top 19 having a threaded portion 20 and which is connected to a suitable source of electrical energy through wires 21 and 22. In this type of unit, the heater is removable by unscrewing it. After the mixture passes the heater it discharges through outlet passageway 23 where it comes into contact with thermistor T In FIG. 4 the thermistor T is placed in inlet passageway 24 and the heater 25 is supported within the main portion of the passageway by supports 26 and 27. The thermistor T is disposed in the outlet portion 28 of the passageway.

FIG. 2 illustrates one type of signal conditional device 15 which can be employed in the practice of the invention. In the device shown, a 20 turn 1000 ohm balancing potentiometer 29 is electrically connected to a 1.3 volt mercury cell 30 through line 31. The opposite ends of the resistor elements of said potentiometer are connected through lines 32 and 33 to matched thermistors T, and T respectively. The thermistors are electrically connected through lines 34,34 to line 35 which is electrically connected to the other side of the cell 30. A millivolt meter 16 is connected across the potentiometer 29 and is calibrated so that changes in voltage will be recorded as precent NVM in the mixutre being tested.

The following example illustrates the practical application of the invention in controlling the solids content of a bath employed for the electrodeposition of paint.

EXAMPLE The paint used has the following composition:

Ingredients Parts by Weight Water soluble acrylic resin (butyl acrylate-styrene-methacrylic acid polymer solution in water 90% solids) 1 18.4 Iron Oxide Pigment 19.7 Ethylene glycol monobutylether l 1.8 Melamine resin (Cymel 300) 28.2 Distilled water 695 This composition is employed with an electroplating bath for depositing paint on ferrous metal surfaces. The bath is operated at a temperature of 77F. with a current density of 2.5 amperes per square foot. 881.3 pounds of the aforesaid composition produces 102.8 gallons of bath.

The bath is connected to a monitoring device of the type shown in FIG. 4 in which T and T are YSI l percent matched thermistors having a base resistance of 1000 ohms (No. 44003) and the heater 25 is a watt 250 ohm heater. The bath is connected to the monitoring device by means of suitable plastic tubing and a pump is placed in the line to recirculate the paint supply from the bath through the monitoring device and back to the bath at a relatively low flow rate of 1.2 gallons per hour. The amount of heat supplied is suffrcient to raise the temperature of the paint composition being tested from 77F. to 86F.i0.5F. The system described with respect to FIGS. 1 and 2 is used to record on a millivolt meter the change in resistance in terms of millivolts.

Meter readings for various solids contents are as follows:

Per Cent Solids By Weight Readings in Millivolts 7.85

turn means that the solids content of the bath is decreasing. The amount of solids required to replenish the bath can readily be determined from the meter reading. Ordinarily, the bath is not allowed to drop more than 2 or 3 percent in solids content before being replenished, and it is preferable to have the meter or other indicating device connected to suitable operating means in order automatically to .maintain the solids content of the bath at the desired level. The addition of the necessary solids can be either intermittent or continuous.

In a small cell having a capacity of 5 gallons of the paint composition and adapted to electrodeposit a coating of one mil thickness on 50 to square feet of steel at a rate of four square feet per minute, additions of solids are required after about 10 to 15 minutes of operation in order to maintain a desirable electrolyte composition. Similar considerations apply to larger scale operations. The invention therefore makes it possible to maintain a non-volatile matter content of an electrodeposition bath by monitoring the change in electrical resistance of the resistance elements in the bath at different temperatures.

It will be recognized that the invention is subject to a number of modifications and variations without departing from the general principles involved. Thus, different types of transducers can be employed, such as nickel resistors. Different types of signal conditioning systems can be used, such as transistorized amplifiers. Self-heated resistors can be employed. The determination of the NVM can also be made by using a resistance heater and ascertaining the number of watts required to produce the desired temperature differential.

The amount of temperature differential desirable to obtain suitable readings will depend to some extent on the type of instrumentation used to amplify and translate the readings. As a practical matter, the temperature differential is preferably such as to give a difference of 0.015F. for each 1 percent NVM to 2F. per percent NVM.

The invention is useful in many different applications where it is desirable to monitor the non-volatile matter content of a mixture containing non-volatile matter in a carrier liquid. These applications include not only paint or coating compositions but also oils containing nonvolatile matter carried in pipe lines or in refineries and other similar applications.

One advantage of this particular type of monitoring apparatus, especially where the mixture being monitored is an electrodeposition bath, is that the operation of the apparatus is not substantially affected by the current in the bath so long as the amount of current is low enough to produce no significant heating effect on the input temperature of the NVM containing fluid.

It should be noted that the presence of cosolvents, such as ethylene glycol monobutylether in the example given, which are not part of the non-volatile matter, does not have any significant effect on the NVM readings as long as their concentration remains relatively constant.

The apparatus provided in accordance with the invention is relatively simple and inexpensive.

I claim:

1. A process for determining the non-volatile matter content of a paint supply comprising a mixture of nonvolatile matter in a liquid carrier which comprises passing a sample of said mixture at a predetermined rate of flow through a tubular passageway, introducing a predetermined amount of heat into said liquid in said passageway sufficient to provide a temperature differential between the temperature adjacent the inlet of said passageway and the temperature adjacent the outlet of said passageway, contacting said liquid adjacent the inlet and outlet with thermally responsive resistors, and translating the change in electrical resistance of said resistors into a measurement of concentration of non-volatile matter in said mixture.

2. A process as claimed in claim 1 in which said sample is heated while flowing it through a tubular passageway and the electrical resistance of said electrical resistance elements before and after heating is measured by a pair of matched thermistors.

3. A process as claimed in claim 2 wherein said matched thermistors are electrically connected to a signal conditioning device responsive to changes in electrical resistance and said signal conditioning device is electrically connected to an indicating device calibrated to read per cent by weight non-volatile matter.

4. A process as claimed in claim 1 wherein said mixture is an aqueous electrodeposition paint.

5. A process as claimed in claim 1 in which the differential temperature before and after heating is at least F.

6. A process as claimed in claim 1 in which said sample is removed from a main body of said mixture and recycled to said main body after said determination of solids content has been made,

7. A process as claimed in claim 6 in which said main body is an aqueous electrodeposition paint bath.

8. An apparatus for determining the non-volatile matter content of a paint'supply comprising a mixture of non-volatile matter in a liquid carrier, which comprises a paint supply of said mixture, means forming a tubular passageway having an inlet connected to said paint supply and an outlet for said mixture, means for pumping said mixture at a predetermined rate through said passageway, heating means for introducing a predetermined amount of heat into said mixture in said passageway, first thermally responsive electrical resistance measuring means in said passageway adapted to contact said mixture before said mixture has been heated by said heating means, second thermally responsive electrical resistance measuring means in said passageway adapted to contact said mixture after said mixture has been heated by said heating means, and means connected to said first and second thermally responsive electrical resistance measuring means to translate the difference in electrical resistance at different temperatures of said measuring means into a measurement of concentration of non-volatile matter in said mixture.

9. An apparatus as claimed in claim 8 in which said first and second thermally responsive electrical resistance measuring means comprise a pair of matched thermistors.

10. An apparatus as claimed in claim 8 comprising a mixing chamber ahead of each of said first and second thermally responsive electrical resistance measuring means.

11. An apparatus as claimed in claim 8 comprising means for pumping said mixture through said tubular passageway.

12. An apparatus as claimed in claim 8 comprising signal conditioning means responsive to a change in electrical resistance connected to said first and second thermally responsive electrical resistance measuring means.

13. An apparatus as claimed in claim 8 comprising means for recycling said mixture from a main body thereof through said passageway and back to said main body. 

1. A process for determining the non-volatile matter content of a paint supply comprising a mixture of non-volatile matter in a liquid carrier which comprises passing a sample of said mixture at a predetermined rate of flow through a tubular passageway, introducing a predetermined amount of heat into said liquid in said passageway sufficient to provide a temperature differential between the temperature adjacent the inlet of said passageway and the temperature adjacent the outlet of said passageway, contacting said liquid adjacent the inlet and outlet with thermally responsive resistors, and translating the change in electrical resistance of said resistors into a measurement of concentration of non-volatile matter in said mixture.
 2. A process as claimed in claim 1 in which said sample is heated while flowing it through a tubular passageway and the electrical resistance of said electrical resistance elements before and after heating is measured by a pair of matched thermistors.
 3. A process as claimed in claim 2 wherein said matched thermistors are electrically connected to a signal conditioning device responsive to changes in electrical resistance and said signal conditioning device is electrically connected to an indicating device calibrated to read per cent by weight non-volatile matter.
 4. A process as claimed in claim 1 wherein said mixture is an aqueous electrodeposition paint.
 5. A process as claimed in claim 1 in which the differential temperature before and after heating is at least 10*F.
 6. A process as claimed in claim 1 in which said sample is removed from a main body of said mixture and recycled to said main body after said determination of solids content has been made.
 7. A process as claimed in claim 6 in which said main body is an aqueous electrodeposition paint bath.
 8. An apparatus for determining the non-volatile matter content of a paint supply comprising a mixture of non-volatile matter in a liquid carrier, which comprises a paint supply of said mixture, means forming a tubular passageway having an inlet connected to said paint supply and an outlet for said mixture, means for pumping said mixture at a predetermined rate through said passageway, heating means for introducing a predetermined amount of heat into said mixture in said passageway, first thermally responsive electrical resistance measuring means in said passageway adapted to contact said mixture before said mixture has been heated by said heating means, second thermally responsive electrical resistance measuring means in said passageway adapted to contact said mixture after said mixture has been heated by said heating means, and means connected to said first and second thermally responsive electrical resistance measuring means to translate the difference in electrical resistance at different temperatures of said measuring means into a measurement of concentration of non-volatile matter in said mixture.
 9. An apparatus as claimed in claim 8 in which said first and second thermally responsive electrical resistance measuring means comprise a pair of matched thermistors.
 10. An apparatus as claimeD in claim 8 comprising a mixing chamber ahead of each of said first and second thermally responsive electrical resistance measuring means.
 11. An apparatus as claimed in claim 8 comprising means for pumping said mixture through said tubular passageway.
 12. An apparatus as claimed in claim 8 comprising signal conditioning means responsive to a change in electrical resistance connected to said first and second thermally responsive electrical resistance measuring means.
 13. An apparatus as claimed in claim 8 comprising means for recycling said mixture from a main body thereof through said passageway and back to said main body. 